In the case of the non-magnetic single component development method, the structure of a developing device is simple, since the consumption volume of a developer is reduced because of using no carrier and the like, but toner only as a developer, and a mechanism of charging via friction between toner and a developing roller or a thin layer formation plate is employed. Accordingly, the non-magnetic single component development method is suitable for color image formation, since a compact size developing device is possible to be produced, and no magnetic material is further contained in toner in comparison to the case of a magnetic single component development method.
However, only a part has been turned into actual utilization in view of practical application of the electrographic image formation apparatus as a whole, despite the fact that many trials to put into practical application have been attempted so far.
This was attributed to the fact that a developing roller to play a major role for charge and development of toner was difficult to be produced, resulting in unstable performance of the developing roller.
One of the desired properties of the developing roller is to form a thin layer of toner and transport it in good condition, and needless to say, this is to be an important factor to obtain high image quality by charging the toner evenly.
Even though excellent results in toner conveyance performance of the developing roller are obtained at ambient temperature and normal humidity, however, the toner tends to be excessively conveyed at low-temperature and humidity since the amount of residual charge is increased, whereby the toner adhesion to the developing roller is also increased.
As to non-magnetic single component development, problems such as toner leakage, generation of fog on an image and toner fused onto a sleeve are produced both in contact development and in non-contact development, once the toner is excessively conveyed. In the case of the contact non-magnetic single component development, a problem such that the toner is fused onto a sleeve is particularly easy to be produced, and in the case of the non-contact non-magnetic single component development, a toner leakage problem tends to be produced.
(Patent Document 1) Japanese Patent O.P.I. Publication No. 2002-357949
(Patent Document 2) Japanese Patent O.P.I. Publication No. 2001-356587
(Patent Document 3) Japanese Patent O.P.I. Publication No. 8-190263